Background: Osteoarthritis (OA) is one of the ten disabling diseases affecting 9.6% of men and 18 % of women aged over 60 worldwide. OA characterized by articular cartilage loss, subchondral bone remodeling, soft tissue damage and low-grade synovitis It is the most common form of arthritis and major cause of disability in the adult population. The main source of resistin in humans is mononuclear cells. Evidence has shown that higher serum levels of resistin in patients with severe OA compared to controls with no OA and resistin are detected in both serum and synovial fluid, proving its systematical and local involvement in inflammatory changes of OA. Aim of the Work: The aim of this work is to study the effect of local GC intra articular injection on the level of serum resistin in OA knees. Also, to study the relation between different serum levels of resistin and US findings of the knee. Patients and Methods: The ethical approval was obtained from the hospital ethical research committee and each patient entering the study will sign an informed consent. Thirty patients with primary knee OA will be recruited for the study from the Physical medicine, 'Rheumatology and Rehabilitation Outpatient Clinic of Al-Azhar University Hospitals starting from November 2017 till may 2018. In this study we measure Serum Resistin level and Musculoskeletal ultrasound examination of the knee before and three months after steroid injection Results: Serum resistin level is markedly decreased after intra articular steroid injection into OA knee joint. Conclusion: Our study revealed that: Resistin could be considered as an important severity marker of knee OA. Serum resistin level is markedly decreased after intra articular steroid injection into OA knee joint. The longer the duration of illness the higher the resistin level. The older the age the higher the resistin level. The longer the duration of illness, the higher the radiological grade. Serum resistin level should be equal to or higher than 2.8 ng / ml to diagnose a case of primary knee OA